1. Field of the Invention
The invention relates to a strapping machine for strapping a stack of products, in particular a stack of periodicals or the like, by means of a strapping tape.
2. Background Art
Conventional strapping machines comprise a work table on which a longitudinal and/or cross wrapping device is arranged. These devices are generally provided with a closed tape guide frame into which the stack of products is driven. For longitudinal strapping, it is necessary to remove the guide duct portions of the tape guide frame standing in the conveyance path in a suitable manner from the conveyance path so that the stack of products can be driven into the tape guide frame along its conveyance path.
In addition to various hinged versions, a particularly suitable configuration of the tape guide frame for these duct portions which are to be removed is known from DE 195 03 112 A1 and from European patent EP 0 725 005 B1 belonging to the Applicant, in which the tape guide duct portions standing in the conveyance path are simply omitted. The strapping tape is shot via these resultant free air gaps. Parallel to the longitudinal direction, the tape is guided into a duct portion corresponding to the upper horizontal web of the tape guide frame and is then shot on down again via the free air gap.
A particular problem with the strapping, in particular of stacks of periodicals, is that the individual copies in the stack only rest on one another prior to strapping of the stack, and slipping and a breakdown of the stack is prevented only by the friction between them. Therefore, the introduction of the unstrapped stack has to be carried out very cautiously and carefully using the conveyors integrated in the work table.
Starting from this problem, the object of the invention is to develop a strapping machine in such a way that reliable and clean conveyance of the stack of products is guaranteed, in particular in the not yet strapped state.
This object is achieved in that the conveyor used to advance the stack of products is provided with guide walls which flank the stack of products on both sides in the conveyance direction and resemble conveyor belts and with respective feed plates mounted thereon. The guide walls hold and guide the stack of products during conveyance and, at the same time, assist its forward movement. The stack is actually propelled by the feed plates which are mounted on the guide walls and act on the face of the stack directed against the direction of conveyance.
In combination with the special strapping device without guide duct portions standing in the conveyance path of the stack of products, a cleanly defined conveyance path of the stack of products through the strapping machine is obtained with which no tape duct portions which have to be driven laterally out of the conveyance path and therefore come into contact with the lateral guide walls have to be provided.
The controller for the defined control of the conveyor with respect to the speed of the guide walls and position of the feed plates is particularly advantageous in this connection. The term xe2x80x9cdefined controlxe2x80x9d means that the position of the feed plates and the speed of the guide walls are monitored throughout operation of the conveyor. The conveyor can therefore be operated continuously so the stack of products can be handled optimally. For example, a virtually xe2x80x9cflying exchangexe2x80x9d of the stack of products into the conveyor of the strapping machine can take place during the transfer of the stack of products from a delivery device of a component positioned before the strapping machine according to the invention, for example a packaging line. The speed of the guide walls can be adapted to the entry speed of the stack of products. Simultaneous control can be carried out in such a way that the feed plates virtually xe2x80x9ccatch up withxe2x80x9d the stack of products from the entry side and approach the stack of products gently from behind. Therefore, the stack of products does not suffer any impacts as a result of impinging against stationary guide or stop elements in the entry region of the strapping machine.
Package stops which define the strapping position for the stack of products in the machine are also provided in stacking machines. A gentle approach can also be guaranteed by means of the conveyor according to the invention in conjunction with these machine elements. The feed plates simultaneously act as rebound preventers and prevent the elements of the stack from shooting back owing to the package stop.
Although considerably improved handling of the stack of products in the strapping machine can be obtained by the conveyor specified above, some products that are to be strapped nevertheless pose some problems. These are in particular rather irregular stacks of periodicals that exhibit an extremely inhomogeneous structure of the individual periodical and thus of the entire stack due to leaflets of varying format and thickness being inserted. When these periodicals are piled up, the stack very often spreads out so that it is fit for subsequent looping only to a limited extent. In particular, the edges of the periodicals that stand out are doubled up or crushed in these stacks, which negatively affects the clean appearance of the paper.
For this problem to be solved, a preferred embodiment provides that the conveyor-belt-type guide walls that flank the stack of products are mounted on the machine for displacement crosswise of the conveyance direction and can be set moving transversely to the stack of products by driving means. This transverse motion may be in particular a transverse upsetting motion i.e., the two guide walls are moved towards each other, pressing the stack of products together.
As a result of this further development of the strapping machine, the spread out individual periodicals of the stack are shoved together for impeccable looping of the cleanly layered stack to take place subsequently.
The transverse motion of the guide walls may as well be used for transverse displacement of the stack of periodicals so that two strapping jobs may take place in parallel and chronologically out-of-line in the strapping device. This is of advantage in particular for the stacks classified as posing problems.
In keeping with further preferred embodiments, the driving means can set the entire conveyor-belt-type guide walls of the conveyor in oscillating, transverse upsetting motion, to which end the return rollers for the guide walls or a support therefor are displaceably mounted and the driving means engage therewith. The driving means may preferably be a pneumatic cylinder.
An alternative of this configuration resides in that the inward strand, applicable to the stack of products, of the conveyor belt that constitutes the respective guide wall is actuated by an eccentric rotor so that the guide wall itself is set in vibration crosswise of its plane of expanse, causing the crosswise upsetting.